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Aims: Plant and soil nitrogen (N) isotope ratios (δ15N) have been used as indicators of N cycling processes of ecosystems. However, the effects of N and Phosphorus (P) addition on δ15N values and their indicative roles in N-cycling in legume-dominated tropical forests remain poorly understood. Methods: We compared leguminous (Acacia auriculiformis) and non-leguminous (Eucalyptus urophylla) forests in terms of N concentration and δ15N in the leaf–litter–soil continuum under long-term N and P addition. Typical soil N-cycling processes, including rates of mineralization, nitrification, and N loss, were also examined to determine the differences between the corresponding 15N signatures observed in the leguminous and non-leguminous forests. Results: The plants in both tropical forests were found to be 15N-depleted. N addition significantly increased the foliage δ15N in understorey species in the non-leguminous but not the leguminous forest. In both forests, the addition of N resulted in an increase in nitrate (NO3−) leaching and nitrous oxide (N2O) emission. Conversely, P addition led to a decrease in NO3− leaching and N2O emission. Additionally, foliage δ15N was positively correlated with soil N loss rates (N2O emission and NO3− leaching) in the non-leguminous forest but showed no correlation in the leguminous forest. Conclusions: In contrast to the traditional convention derived from non-leguminous forests, our results suggest that foliar 15N isotope signals are not applicable for indicating the soil N dynamic status of leguminous forests. This study highlights the importance of distinguishing legumes from other plant species in terrestrial N-cycling models when incorporating 15N isotope signals. [ABSTRACT FROM AUTHOR]

Background and aims: Increased nitrogen (N) deposition may exacerbate soil phosphorus (P) deficiency, which alters soil greenhouse gas (GHG) emissions by changing soil properties and understory vegetation in subtropical forests. However, the effects of N addition, P addition, and understory vegetation interactions on soil carbon dioxide (CO2) and nitrous oxide (N2O) emissions in forest ecosystems and their underlying mechanisms remain unclear. Methods: We conducted a continuous N and P addition experiment in a subtropical Chinese fir plantation. The effects of N and P addition on soil CO2 and N2O emissions with different understory vegetation were examined using a structural equation model. Results: The addition of N and P did not directly affect soil CO2 emission of the understory, which was affected by understory species (F = 2.86; p = 0.05). N indirectly and positively affects soil CO2 emission through plant elements, and directly affect N2O emission of understory soil. Compared with CK, the addition of N2 promoted the N2O cumulative emission by 74.3%. N has a direct positive effect on soil N2O emissions, while P addition indirectly exerts a negative influence on N2O emissions through its impact on soil properties. Plant elements and soil properties were explained in 26.3% of soil CO2 emissions, of which 17.6% and 16.0% variations were explained by plant elements and soil properties, respectively. Leaf total N was the most important factor for predicting CO2 emissions. Conclusions: Our results suggested that soil CO2 emission was more dependent on plant elements, and soil N2O emission was directly dependent on N addition rather than plant elements. Thus, different patterns of soil GHG emissions and associated controls following N and P addition provided novel insights into predicting the effects of understory vegetation on climate change mitigation outcomes. [ABSTRACT FROM AUTHOR]

Increasing nitrogen (N) deposition alters the availability of soil nutrients and is likely to intensify phosphorus (P) limitations, especially in P-limited tropical and subtropical forests. Soil microorganisms play vital roles in carbon (C) and nutrient cycling, but it is unclear whether and how much N and P imbalances affect the soil's microbial metabolism and mechanisms of nutrient limitations. In this study, a 3-year field experiment of N and P addition (control (CK), 100 kg N ha−1 yr−1 (N), 50 kg P ha−1 yr−1 (P), and NP) was set up to analyze the extracellular enzyme activities and stoichiometry characteristics of the top mineral soils in Chinese fir plantations with different stand ages (7, 20, and 33 years old). The results showed that the enzyme activities associated with the acquisition of C (β-1,4-glucosidase (BG) and β-d-cellobiohydrolase (CBH)) and P (acid phosphatases (APs)) in the N treatment were significantly higher than those in the CK treatment. Moreover, vector analysis revealed that both the vector's length and angle increased in stands of all ages, which indicated that N addition aggravated microbial C and P limitations. The P and NP treatments both significantly decreased the activity of AP and the enzymes' N:P ratio, thereby alleviating microbial P limitations, as revealed by the reduction in the vector's angle. Stand age was found to promote all enzymatic activities but had no obvious effects on the limitation of microbial metabolism with or without added nutrients in the soils under Chinese fir. Available N, Olsen-P, and pH were the main drivers of microbial metabolic limitations related to C nutrients. These results provide useful data for understanding the change in soil microbial activity in response to environmental changes, and suggest that P fertilization should be considered for management to improve productivity and C sequestration in Chinese fir plantation in the context of increased deposition of N. [ABSTRACT FROM AUTHOR]

The phenomenon of nitrogen deposition resulting in species loss in terrestrial ecosystems has been demonstrated in several experiments. Nitrogen (N) and phosphorus (P), as major nutrients required for plant growth, exhibit ecological stoichiometric coupling in many ecosystems. The increased availability of nitrogen can exacerbate the ecological effects of phosphorus. To reveal the ecological effects of phosphorus under nitrogen-limiting and non-limiting conditions, we conducted a controlled N-P interaction experiment over 5 years in the Hulunbuir meadow steppe, where two nitrogen addition levels were implemented: 0 g N·m-2·a-1 (nitrogen-limiting condition) and 10 g N·m-2·a-1 (nitrogen-non-limiting condition), together with six levels of phosphorus addition (0, 2, 4, 6, 8, and 10 g P·m-2·a-1). The results showed that nitrogen addition (under nitrogen-non-limiting conditions) significantly decreased species diversity in the steppe community, which was exacerbated under phosphorus addition. Under nitrogen-limiting conditions, phosphorus addition had no marked impact on species diversity compared to the control; however, there were substantial differences between different levels of phosphorus addition, exhibiting a unimodal change. Under both experimental nitrogen conditions, the addition of 6 g P·m-2·a-1 was the threshold for affecting the community species diversity. Nitrogen addition reduced the relative biomass of legumes, bunch grasses, and forbs, but substantially increased the relative biomass of rhizomatous grasses. In contrast, phosphorus addition only markedly affected the relative biomass of forbs and rhizomatous grasses, with the former showing a unimodal pattern of first increasing and then decreasing with increasing phosphorus addition level, and the latter exhibiting the opposite pattern. The different responses of rhizomatous grasses and other functional groups to nitrogen and phosphorus addition were observed to have a regulatory effect on the changes in grassland community structure. Phosphorus addition may increase the risk of nitrogen deposition-induced species loss. Both nitrogen and phosphorus addition lead to soil acidification and an increase in the dominance of the already-dominant species, and the consequent species loss in the forb functional group represents the main mechanism for the reduction in community species diversity. [ABSTRACT FROM AUTHOR]

Abiotic resource limitation presents organisms with a dilemma about how to use resources when they become available. Characterizing how resource allocation affects investment in growth or defensive traits that affect organismal survival strategies allows us to understand the environmental contexts in which species interact. Our goal was to measure how macronutrient availability drives nitrogen and phosphorus allocation towards functional growth and defensive chemical traits of the Neotropical passion vine, Passiflora biflora.We investigated this question with a paired field study in La Selva, Costa Rica and a full factorial greenhouse experiment to determine whether the concentration of a key secondary chemical defence is driven by nitrogen availability. We correlated defensive chemical concentration with soil nitrogen availability in naturally occurring plants, measured the effects of nitrogen and phosphorus availability on growth and secondary chemical defence traits in the greenhouse and characterized the P. biflora leaf metabolome to assess how nutrient availability affected shifts in metabolism related to plant fitness.We found that nutrient allocation increased the magnitude of both growth and defence traits. Increased nitrogen availability resulted in higher concentrations of toxic leaf secondary chemicals, longer vines, greater biomass and more leaves with a superior ability to capture sunlight. In addition, plants from high nitrogen environments had metabolomes with significantly greater secondary metabolite richness and biochemical pathway diversity, as well as increases in the number of metabolites from several chemical classes related to basic cell function and defence. Nutrient availability had no significant effect on the richness and diversity of primary metabolites involved in basic cell functions. A direct comparison of the relative strength of quantitative growth and secondary defence traits indicated that P. biflora favours nutrient allocation to growth at low nitrogen levels but invests in both strategies more evenly as nitrogen availability increases.These findings lead us to predict that passion vines are better prepared to tolerate and resist herbivory when nutrients are plentiful and experience a trade‐off between growth and chemical defence against natural enemies when they are scarce. These findings are consistent with both the 'escape' and 'defend' syndromes that are often used to describe tropical plant survival strategies. This is one of the only studies to measure nutrient allocation in vines, a group comprising a significant percentage of global plant diversity. Moreover, this work demonstrated the power of leveraging untargeted metabolomics to characterize how nutrient addition affects plant growth and defence, highlighting its potential for understanding functional trait variation. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Introduction: Understanding the response of cross-domain co-occurrence networks of soil microorganisms to phosphorus stability and the resulting impacts is critical in ecosystems, but the underlying mechanism is unclear in artificial grassland ecosystems. Methods: In this study, the effects of four phosphorus concentrations, P0 (0 kg P ha-1), P1 (15.3 kg P ha-1), P2 (30.6 kg P ha-1), and P3 (45.9 kg P ha-1), on the cross-domain co-occurrence network of bacteria and fungi were investigated in an artificial Leymus chinensis grassland in an arid region. Results and discussion: The results of the present study showed that phosphorus addition significantly altered the stem number, biomass and plant height of the Leymus chinensis but had no significant effect on the soil bacterial or fungal alpha (ACE) diversity or beta diversity. The phosphorus treatments all increased the cross-domain co-occurrence network edge, node, proportion of positively correlated edges, edge density, average degree, proximity to centrality, and robustness and increased the complexity and stability of the bacterial-fungal cross-domain co-occurrence network after 3 years of continuous phosphorus addition. Among them, fungi (Ascomycota, Basidiomycota, Mortierellomycota and Glomeromycota) play important roles as keystone species in the cooccurrence network, and they are significantly associated with soil AN, AK and EC. Finally, the growth of Leymus chinensis was mainly due to the influence of the soil phosphorus content and AN. This study revealed the factors affecting the growth of Leymus chinense in artificial grasslands in arid areas and provided a theoretical basis for the construction of artificial grasslands. [ABSTRACT FROM AUTHOR]

Introduction: Phosphorus (P), which plays a vital role in plant growth, is continually added to soil to maximize biomass production, leading to excessive P accumulation and water eutrophication. Results: In this study, a pot experiment using a subtropical tobacco-growing soil fertilized with four P levels—no P, low P, medium P, and high P—was conducted and rhizosphere and bulk soils were analyzed. Results: P addition significantly increased tobacco biomass production (except under low P input) and total soil P and available P content (P<0.05), whereas total nitrogen content decreased in the rhizosphere soils, although this was only significant with medium P application. P fertilization also significantly altered the bacterial communities of rhizosphere soils (P<0.05), but those of bulk soils were unchanged (P>0.05). Moreover, a significant difference was found between rhizosphere soils with low (LR) and high (HR) P inputs (P<0.05). Additionally, compared with rhizosphere soils with no P (CKR), Shannon diversity showed a declining trend, which was significant with LR and HR (P<0.05), whereas an increasing tendency was observed for Chao1 diversity except in LR (P>0.05). Functional prediction revealed that P application significantly decreased the total P and N metabolism of microorganisms in rhizosphere soils (P<0.05). Discussion: Collectively, our results indicate that maintaining sustainable agricultural ecosystems under surplus P conditions requires more attention to be directed toward motivating the potential of soil functional microbes in P cycling, rather than just through continual P input. [ABSTRACT FROM AUTHOR]

Background and aims: Phosphorus (P) addition is considered key factor in soil organic carbon (SOC) cycle. The potential impact mechanisms of P addition on SOC stability and sequestration were explored in saline-alkali soil. Methods: A 9-year field experiment was arranged in the Yellow River Delta, which included (i) CK, no fertilization; (ii) NK, N and K fertilizer application; (iii) NP1K and (iv) NP2K, NK plus 28 and 56 kg P ha−1 year−1 application, respectively. Results: Compared with NK, the content of particulate OC (POC) was significantly increased by 29.9% and 26.8% in NP1K and NP2K treatments, respectively. The variation trend of aromatic-C and microbial biomass C (MBC) was similar to that of POC, which were positively corelated with SOC sequestration. Meanwhile, C and specific C mineralization rate (CMR, SCMR) were increased with P addition, which might be due to the decrease of carboxyl or amidogen-C. Moreover, owing to the increase in root biomass, SOC sequestration was significantly increased by more than 9.3% with P addition. Redundancy analysis further indicated that root biomass was the main factor in regulating SOC. While the CMR and SCMR were higher of NP2K treatment than those of NP1K treatment, this might result in SOC sequestration was no significant change between the two treatments. Conclusion: Long-term low-level P fertilization is a preferable practice to increase POC, stable chemical composition and MBC, and then SOC sequestration. These findings provide important insights into how long-term different levels of P application regulate soil C cycling in saline-alkali paddy soil. [ABSTRACT FROM AUTHOR]

The escalation of global nitrogen deposition levels has heightened the inhibitory impact of phosphorus limitation on plant growth in subtropical forests. Plant roots area particularly sensitive tissue to nitrogen and phosphorus elements. Changes in the morphological characteristics of plant roots signify alterations in adaptive strategies. However, our understanding of resource-use strategies of roots in this environment remains limited. In this study, we conducted a 10-month experiment at the Castanopsis kawakamii Nature Reserve to evaluate the response of traits of seedling roots (such as specific root length, average diameter, nitrogen content, and phosphorus content) to nitrogen and phosphorus addition. The aim was to reveal the adaptation strategies of roots in different nitrogen and phosphorus addition concentrations. The results showed that: (1) The single phosphorus and nitrogen–phosphorus interaction addition increased the specific root length, surface area, and root phosphorus content. In addition, single nitrogen addition promotes an increase in the average root diameter. (2) Non-nitrogen phosphorus addition and single nitrogen addition tended to adopt a conservative resource-use strategy to maintain growth under low phosphorus conditions. (3) Under the single phosphorus addition and interactive addition of phosphorus and nitrogen, the roots adopted an acquisitive resource-use strategy to obtain more available phosphorus resources. Accordingly, the adaptation strategy of seedling roots can be regulated by adding appropriate concentrations of nitrogen or phosphorus, thereby promoting the natural regeneration of subtropical forests. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) not only contributes to maintain soil health, but is also important in regulating global climate change. How atmospheric nitrogen (N) deposition and phosphorus (P) addition affects SOC dynamics remains unclear, especially in subtropical forests. The response of SOC in three layers to N deposition and P addition in this study is estimated by analyzing the soil aggregates and C chemical stability composition fertilized with N (100 kg N hm−2 a−1) and/or P (50 kg P hm−2 a−1) over 9 years in a Chinese fir (Cunninghamia lanceolata) plantation. Treatments involving N deposition increased the SOC concentration, while P addition alone decreased the SOC concentration in soil layers above 10 cm. The addition of N significantly increased the mean diameter of topsoil aggregates, macroaggregates SOC concentration, and the contribution of N to total SOC. P addition decreased the relative abundances of aromatic and aliphatic functional groups while decreasing the chemical stability of SOC in the topsoil. A structural equation model indicated that N deposition promoted SOC concentration by mainly improving the physical protection of soil aggregates, while P addition reduced SOC sequestration by decreasing the chemical stability of SOC. Our research suggested that elevated N deposition might promote the soil C sink, while P fertilization would not be recommended under increased N deposition to protect soil C storage in subtropical forests. [ABSTRACT FROM AUTHOR]

Increasing nitrogen (N) deposition alters the availability of soil nutrients and is likely to intensify phosphorus (P) limitations, especially in P-limited tropical and subtropical forests. Soil microorganisms play vital roles in carbon (C) and nutrient cycling, but it is unclear whether and how much N and P imbalances affect the soil’s microbial metabolism and mechanisms of nutrient limitations. In this study, a 3-year field experiment of N and P addition (control (CK), 100 kg N ha−1 yr−1 (N), 50 kg P ha−1 yr−1 (P), and NP) was set up to analyze the extracellular enzyme activities and stoichiometry characteristics of the top mineral soils in Chinese fir plantations with different stand ages (7, 20, and 33 years old). The results showed that the enzyme activities associated with the acquisition of C (β-1,4-glucosidase (BG) and β-d-cellobiohydrolase (CBH)) and P (acid phosphatases (APs)) in the N treatment were significantly higher than those in the CK treatment. Moreover, vector analysis revealed that both the vector’s length and angle increased in stands of all ages, which indicated that N addition aggravated microbial C and P limitations. The P and NP treatments both significantly decreased the activity of AP and the enzymes’ N:P ratio, thereby alleviating microbial P limitations, as revealed by the reduction in the vector’s angle. Stand age was found to promote all enzymatic activities but had no obvious effects on the limitation of microbial metabolism with or without added nutrients in the soils under Chinese fir. Available N, Olsen-P, and pH were the main drivers of microbial metabolic limitations related to C nutrients. These results provide useful data for understanding the change in soil microbial activity in response to environmental changes, and suggest that P fertilization should be considered for management to improve productivity and C sequestration in Chinese fir plantation in the context of increased deposition of N.

[Objective] To investigate the effects of leaf litter, P addition, and their interactions on changes in SOC and SON components.[Method] The effects of three kinds of withered leaf additions（Michelia macclurei, Pinus masson and Liquidam fortiana） and P addition（KH2PO4） on SOC and SON components were investigated through a 125-day indoor culture experiment with the soil of Pinus massoniana as the research object. [Result]The results showed that both leaf litter addition and P addition significantly reduced the content of recalcitrant C（RP-C） component, and they showed a strong interaction. The effects of leaf litter on SOC and SON were influenced by soil P availability, and P addition accelerated the decomposition of original recalcitrant C by soil microorganisms under leaf litter addition. Redundancy analysis showed that ammonia nitrogen（NH+4-N） and available phosphorus（AP） were the most important influencing factors of SOC fraction, while dissolved organic carbon（DON） and microbial biomass phosphorus（MBP） were the most important predictors of SON fraction. [Conclusion] P addition can promote the decomposition and transformation of leaf litter in soil, and the input of leaf litter increases the decomposition of recalcitrant C, which will further accelerate the turnover of SOC. This study will provide a scientific basis for the study of carbon and nitrogen cycling in subtropical soil with increased litter input and P limitation and forest soil management in Daiyunshan Nature Reserve. [ABSTRACT FROM AUTHOR]

Nitrogen (N) and phosphorus (P) addition, either individually or in combination, has been demonstrated to enhance plant productivity in grassland ecosystems. Soil bacterial community, which is the driver of litter decomposition and nutrient cycling, is assumed to control responses of terrestrial ecosystem structure and function to N and P addition. Using a high-throughput Illumina MiSeq sequencing platform, we conducted a 9-year field experiment of N (0, 5, 10, and 20 g N m-2 yr-1) and P (0 and 10 g P m-2 yr-1) additions in the Inner Mongolian steppes to elucidate long-term effects of N and P addition on soil bacterial richness, diversity and composition. We found that N addition reduced the relative abundance of Acidobacteria, Chloroflexi, and Nitrospirae, while increased that of Bacteroides. The results showed that the bacterial biomarker was enriched in P addition treatments, either individually or combined with N addition. Both N and P addition altered the bacterial community structure, while only N addition greatly decreased bacterial richness and diversity. More importantly, we showed that all of these effects were most significant in N3P treatment (20 g N m-2 yr-1 and 10 g P m-2 yr-1), implying that P coupled with a high-level N addition exerted a great influence on soil bacterial community. Structural equation models revealed that N and P addition had a great direct effect on soil bacterial community and an indirect effect on it mainly by changing the litter biomass. Our findings highlighted that severe niche differentiation was induced by P along with a high-level N, further emphasizing the importance of simultaneously evaluating response of soil bacterial community to N and P addition, especially in the context of increasing anthropogenic nutrient additions. [ABSTRACT FROM AUTHOR]

Abstract Introduction Fungal communities are key players in the soil biogeochemical processes of forest ecosystems. Although it has been illustrated that soil fungi are susceptible to environmental changes, little is known about the interactive effects of nitrogen (N) and phosphorus (P) enrichment on the soil fungal functional guild. Materials and Methods Here, a 5‐year N and P addition manipulation experiment was conducted in two growing stages (i.e., tree ages 80 years) of a subtropical forest, in which soil fungal diversity and functional guilds were investigated using a multiple‐time sampling strategy. Results Fungal species richness and Shannon indices were significantly different across sampling times. Fungal community composition was significantly affected by both N and P addition but not by forest age. Old forest had a higher fungal network complexity than young forest, and fertilisation decreased soil fungal network complexity and generated looser and more random networks in comparison with the control. The community composition of symbiotrophic and saprotrophic fungi was significantly impacted by N and P addition and correlated with soil available P and total P contents and soil C:P and N:P. Conclusions Our findings highlight that soil P availability has a strong effect on soil fungal communities and their functional guild composition in the subtropical forest.

Nitrogen (N) and phosphorus (P) are key components in biogeochemical cycling and considerable efforts have been made to understand the effects of their availability on microbial biomass. Nevertheless, the interplay between N and P supply in modulating soil microbes remains unclear. We conducted a comprehensive global analysis of 108 studies spanning boreal to tropical regions to evaluate their interactive impacts on microbial biomass. The findings revealed a significant decrease in microbial biomass with N addition, whereas P supplementation resulted in a notable increase in microbial biomass. Among the observed interactive effects, additive effects were predominant. More importantly, we found that among all of the assessed factors, the impacts of N-P interaction on soil microorganisms are dependent on changes in soil pH. In conclusion, our findings provide valuable insights into the interactive effects of N and P enrichment on microbial biomass. These findings will contribute to the development of global models that predict the impacts of N and P enrichment on soil microbes and ecosystem functions.

Background and aim: Phosphorus (P) addition is a common practice to alleviate P limitation in agricultural ecosystems. However, information regarding microbial communities' response to P addition in grasslands remains limited. The present study aimed to investigate the response of bacterial communities from rhizosphere and root endosphere of Achnatherum inebrians to P addition, and assess the potential roles played by mutualistic endophyte Epichloë gansuensis in these processes. Methods: The response of bacterial communities to P addition was investigated based on 16S rRNA sequencing. Soil properties were determined and Mantel test was employed to evaluate the main factors contributing to bacterial community alteration. Additionally, the root exudates were assessed by GC-MS. Results: P addition influenced the bacterial community composition in both the rhizosphere and root endosphere of A. inebrians with (E+) or without (E−) E. gansuensis, while not affecting community diversity. Moreover, P addition increased the soil available P, total P, and pH levels, which exhibited significant correlation with the bacterial communities in both rhizosphere and root endosphere of A. inebrians. Additionally, P addition increased the exudation of xylose, glycine, alanine, mandelic acid, and lactic acid from E+ plant roots. Conclusions: P addition shapes the bacterial communities in rhizosphere and root endosphere of A. inebrians by altering soil total P, available P, pH levels. Meanwhile, P addition modulates the root exudate profiles that mediated by E. gansuensis. This study provides new insights into the response of plant-soil-microbe ecosystem to P addition, which is helpful for the fertilization management during grassland sustainability. [ABSTRACT FROM AUTHOR]

Background and aims: A synergistic response of aboveground plant biomass production to combined nitrogen (N) and phosphorus (P) addition has been observed in many ecosystems, but the underlying mechanisms and their relative importance are not well known. We aimed at evaluating several mechanisms that could potentially cause the synergistic growth response, such as changes in plant biomass allocation, increased N and P uptake by plants, and enhanced ecosystem nutrient retention. Methods: We studied five grasslands located in Europe and the USA that are subjected to an element addition experiment composed of four treatments: control (no element addition), N addition, P addition, combined NP addition. Results: Combined NP addition increased the total plant N stocks by 1.47 times compared to the N treatment, while total plant P stocks were 1.62 times higher in NP than in single P addition. Further, higher N uptake by plants in response to combined NP addition was associated with reduced N losses from the soil (evaluated based on soil δ15N) compared to N addition alone, indicating a higher ecosystem N retention. In contrast, the synergistic growth response was not associated with significant changes in plant resource allocation. Conclusions: Our results demonstrate that the commonly observed synergistic effect of NP addition on aboveground biomass production in grasslands is caused by enhanced N uptake compared to single N addition, and increased P uptake compared to single P addition, which is associated with a higher N and P retention in the ecosystem. [ABSTRACT FROM AUTHOR]

Aims: Nitrogen (N) and phosphorus (P) have important roles in the terrestrial carbon (C) cycle. Nevertheless, the responses of microbial ecological functions involving C cycling in saline-sodic soils to N and P are barely known, particularly at the functional gene level. Methods: The influence of N and P addition on C functional genes in saline-sodic soils was explored using a pot experiment. Eight treatments were conducted, namely: a control (CK), three N addition levels (NL, NM, and NH), three P addition levels (PL, PM, and PH), and combined N and P addition (NP). Results: Results revealed that the total abundance of C functional genes was enhanced by the addition of N and P, promoting C fixation, degradation, and CH4 metabolism. The total gene abundance was the highest in NL among the three N addition treatments; however, the highest abundance was observed in PH among the three P addition treatments. Compared to CK, all treatments exerted greater effects on the abundance of genes related to recalcitrant C decomposition than on labile C decomposition. This was because increment in relative abundance of oligotrophic taxa was greater than that of copiotrophic taxa after the addition of N and P. Partial least squares path modeling analysis revealed that N and P addition regulated gene abundance by altering DOC, microbial diversity, and ESP, thereby directly influencing C mineralization. Conclusions: Our results highlight that N and P stimulate the abundance of C functional genes via plant biomass and soil property traits in saline-sodic soils. [ABSTRACT FROM AUTHOR]

Rhizosphere is a hot zone formed by root–microbial interaction, and microbial activities in this zone differ from those in bulk soil. Nitrogen (N) and phosphorus (P) inputs are able to change forest soil nutrient availability, affecting microbial communities and extracellular enzyme secretion. However, the impact of N and P additions on the structure and functions of rhizosphere microbial community in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations are not yet clear. To reveal the impact of short-term N and P inputs on microbial community structure and functions in rhizosphere soil, soil physicochemical properties, phospholipid fatty acids, and seven hydrolytic enzyme activities were measured in Chinese fir rhizosphere soil after one year of nutrient addition. N addition reduced the rhizosphere's pH and increased ammonium N, but the rhizosphere's available N (AN) initially wentdown and then up along the P-addition gradient. The rhizosphere fungi:bacteria ratio showed a decline after N addition, while a concave peak change occurred as rhizosphere AN under P addition. Moreover, rhizosphere extracellular enzyme activities and microbial C limitation climbed markedly with N addition rates, while this also showed an obviously unimodal pattern along the P-addition gradient. P addition did not alleviate rhizosphere microbial P limitation. Our findings suggest inconsistent responses of rhizosphere microorganisms of Chinese fir soil to N and P additions. Rhizosphere N availability can regulate microbial community structure and extracellular enzymes by influencing microbial C limitation. The study provides more knowledge on microbial activities in rhizosphere soil of subtropical forests under global changes. [ABSTRACT FROM AUTHOR]

The escalation of global nitrogen deposition levels has heightened the inhibitory impact of phosphorus limitation on plant growth in subtropical forests. Plant roots area particularly sensitive tissue to nitrogen and phosphorus elements. Changes in the morphological characteristics of plant roots signify alterations in adaptive strategies. However, our understanding of resource-use strategies of roots in this environment remains limited. In this study, we conducted a 10-month experiment at the Castanopsis kawakamii Nature Reserve to evaluate the response of traits of seedling roots (such as specific root length, average diameter, nitrogen content, and phosphorus content) to nitrogen and phosphorus addition. The aim was to reveal the adaptation strategies of roots in different nitrogen and phosphorus addition concentrations. The results showed that: (1) The single phosphorus and nitrogen–phosphorus interaction addition increased the specific root length, surface area, and root phosphorus content. In addition, single nitrogen addition promotes an increase in the average root diameter. (2) Non-nitrogen phosphorus addition and single nitrogen addition tended to adopt a conservative resource-use strategy to maintain growth under low phosphorus conditions. (3) Under the single phosphorus addition and interactive addition of phosphorus and nitrogen, the roots adopted an acquisitive resource-use strategy to obtain more available phosphorus resources. Accordingly, the adaptation strategy of seedling roots can be regulated by adding appropriate concentrations of nitrogen or phosphorus, thereby promoting the natural regeneration of subtropical forests.

Soil organic carbon (SOC) not only contributes to maintain soil health, but is also important in regulating global climate change. How atmospheric nitrogen (N) deposition and phosphorus (P) addition affects SOC dynamics remains unclear, especially in subtropical forests. The response of SOC in three layers to N deposition and P addition in this study is estimated by analyzing the soil aggregates and C chemical stability composition fertilized with N (100 kg N hm−2 a−1) and/or P (50 kg P hm−2 a−1) over 9 years in a Chinese fir (Cunninghamia lanceolata) plantation. Treatments involving N deposition increased the SOC concentration, while P addition alone decreased the SOC concentration in soil layers above 10 cm. The addition of N significantly increased the mean diameter of topsoil aggregates, macroaggregates SOC concentration, and the contribution of N to total SOC. P addition decreased the relative abundances of aromatic and aliphatic functional groups while decreasing the chemical stability of SOC in the topsoil. A structural equation model indicated that N deposition promoted SOC concentration by mainly improving the physical protection of soil aggregates, while P addition reduced SOC sequestration by decreasing the chemical stability of SOC. Our research suggested that elevated N deposition might promote the soil C sink, while P fertilization would not be recommended under increased N deposition to protect soil C storage in subtropical forests.

Plant–soil feedback (PSF) is conventionally characterized by plant biomass growth, yet it remains unclear how PSF affects plant nutrient acquisition strategies (e.g. nutrient absorption and nutrient resorption) associated with plant growth, particularly under changing soil environments. A greenhouse experiment was performed with seedlings of Pinus elliottii Englem and conditioned soils of monoculture plantations (P. elliottii and Cunninghamia lanceolata Hook). Soil sterilization was designed to test plant phosphorus (P) acquisition strategy with and without native soil fungal communities. Soils from P. elliottii and C. lanceolata plantations were used to explore the specific soil legacy effects on two different P acquisition pathways (absorption and resorption). Phosphorus addition was also applied to examine the separate and combined effects of soil abiotic factors and soil fungal factors on P acquisition pathways. Due to diminished mycorrhizal symbiosis, PSF prompted plants to increasingly rely on P resorption under soil sterilization. In contrast, P absorption was employed preferentially in the heterospecific soil, where species-specific pathogenic fungi could not affect P absorption. Higher soil P availability diluted the effects of soil fungal factors on the trade-off between the two P acquisition pathways in terms of the absolute PSF. Moreover, P addition plays a limited role in terms of the relative PSF and does not affect the direction and strength of relative PSF. Our results reveal the role of PSF in regulating plant P acquisition pathways and highlight the interaction between mycorrhizal and pathogenic fungi as the underlying mechanism of PSF. [ABSTRACT FROM AUTHOR]

Phosphorus (P) fertilizer is commonly used in subtropical plantations to augment nutrients including carbon (C), nitrogen (N), and P to maintain plants engaged in metabolism. Stoichiometric homeostasis reflects the adaptation of plants to various environments (including P fertilizer supply rates). It is thus of great significance to understand C:N:P stoichiometry in the plant–litter–soil system under P addition and the stoichiometric homeostasis of plant tissues for the P fertilization management of slash pine (Pinus elliottii Engelm) plantations. In subtropical China, we measured the C, N, and P contents in root, branch, needle, litter, and soil in slash pine plantations fertilized with four treatments, P1 (25 kg P ha1 yr1), P2 (50 kg P ha1 yr1), P3 (100 kg P ha1 yr1), and a control (CK), and calculated the stoichiometric homeostasis of plant tissues. The results show that P3 treatment increased the C, N, and P contents of the needle. P2 and P3 treatments increased the P content of the litter and the N:P ratio of the root while decreasing the C:N ratio of the root. P addition treatments increased C and P element accumulation in soil but had no effect on soil stoichiometry. The nutrient contents of needle and branch were higher than those of root and litter, indicating that slash pine was more inclined to allocate nutrients to the aboveground tissues. The stoichiometric homeostasis of C, N, and P among plant tissues was graded as follows: root > branch > needle. The needle's nutritional homeostasis was C > N > P, with 1/H values of 0.08, 0.34, and 0.74, respectively. These findings demonstrate that during P addition, the C, N, and P stoichiometric homeostasis varied among plant tissues and element types. In conclusion, P application altered nutrient distribution in the plant–litter–soil system, alleviating P restriction in slash pine forests in southern China. P addition levels should be finely adjusted in the future for longer-term observation trials, and the trade-off between P addition rates and economic and ecological advantages should be properly examined. [ABSTRACT FROM AUTHOR]

Purpose: Nitrogen (N) and phosphorus (P) amendments considerably influence fungal diversity and community composition in various ecosystems. Nevertheless, how N and P additions would change arbuscular mycorrhizal (AM) fungal community and functional guilds in forest soil remains largely unclear. Materials and methods: A 5-year N and P addition experiment was conducted in a subtropical forest of southeastern China. Soil AM fungal communities were detected by the high throughput sequencing of 18S rRNA gene-fragments. We investigated the six-seasonal responses of AM fungal diversity, community assembly pattern and functional guild composition to N and/or P amendments. Results and discussion: The AM fungal Shannon index changed from a positive (3–4 years) to a nonsignificant (4–5 years) effect under P and NP additions as the duration of fertilization increased. P addition, but not N addition, changed the AM fungal community assembly pattern from stochastic- to deterministic-dominant processes. In contrast, P and NP additions significantly influenced AM fungal functional guild components, and the relative abundances of ancestral and edaphophilic guilds increased with increasing years of fertilization. Additionally, the AM fungal guild structure was significantly affected by soil P-related parameters. Conclusions: Our results emphasize the substantial impacts of P amendment on soil AM community assembly pattern and functional guild composition. This study contributes to a better understanding of the temporal dynamics and potential ecological functioning of AM fungi under global environmental changes. [ABSTRACT FROM AUTHOR]

Greenhouse gas (GHG) emissions from rice paddies have gained widespread attention, and fertilization management can mitigate GHG emissions. Red paddy soils in southern China are characterized by phosphorus (P) deficiency, requiring fertilization management. In the present study, soils from a red paddy field were used in a pot experiment with 5 levels of P application (P1–P5: 0, 22.5, 45, 90, 113, 135 kg ha−1, respectively) to investigate growth and yield of rice (Oryza sativa L.) and carbon dioxide (CO2) and methane (CH4) emissions from soils. P application increased photosynthetic rate, tiller number, plant biomass and yield. All P treatments decreased CH4 emission at the tillering stage but increased it at the filling and maturing stages, causing decreases in cumulative CH4 emission under P1, P2, and P4. Cumulative CO2 emission did not significantly differ among P0–P3 but increased by P4 and P5. Cumulative CO2 and CH4 emissions were positively correlated with plant height, implying that changes in plant structure such as aerenchyma might be attributable to GHG emissions. Overall, P application of 89 kg ha−1 was sufficient to reduce GHG emissions and enhance rice yield. These results provide a reference for adjusting P management in red paddy fields. [ABSTRACT FROM AUTHOR]

Nitrogen (N) and phosphorus (P) nutrients have been regularly applied to improve productivity in intensively managed and short-rotation forest plantations in subtropical China. Under the constraint of the national policy of "carbon neutrality", it is necessary to determine the rational fertilization options by considering both forest productivity and soil CO2 emissions. Past worldwide studies have shown varied responses of forest soil heterotrophic respiration and CO2 emissions to N and P additions. This study designed six treatments with N additions (high level: 15 g N/m2, HN), P (low: 5 g P/m2, LP; high: 15 g P/m2, HP), and their interactions (HNLP and HNHP) to explore the effects of N and P additions on soil CO2 emissions in a P-limited and N-rich Chinese fir plantation (Cunninghamia lanceolata), and we identified the underlying controls using the structural equation model (SEM). The results indicated that LP, HNLP, and HNHP treatments significantly increased soil CO2 emissions in the first four months after treatment and the effects leveled since then. The balance between N and P inputs affected the responses of soil CO2 emissions to P additions. A low P addition significantly increased tree productivity, but the promoting effect gradually declined and was no longer significant after 3 years. Other treatments did not significantly affect tree productivity. The SEM analysis revealed that the promoting effects of P additions on CO2 emission were mainly due to their effects on increasing soil water-soluble organic carbon content and reducing microbial biomass nitrogen content. Considering both soil respiration and tree productivity, this study suggested that LP treatment can effectively balance the N and P nutrients and, in the meantime, maintain relatively low greenhouse gas emissions; thus a low P application level is suggested for N-rich Chinese fir plantations. [ABSTRACT FROM AUTHOR]

Background and Aims Growing evidence has suggested that plant responses to model soil microorganisms are context dependent; however, few studies have investigated the effects of whole soil microbial communities on plant performance in different abiotic and biotic conditions. To address this, we examined how soil phosphorus (P) availability and different planting patterns regulate soil microbial effects on the growth of two native plant species in a semiarid steppe. Methods We carried out a glasshouse experiment to explore the effects of the whole indigenous soil microbiota on the growth and performance of Leymus chinensis and Cleistogenes squarrosa using soil sterilization with different soil P availabilities and planting patterns (monoculture and mixture). Transcriptome sequencing (RNA-seq) was used to explain the potential molecular mechanisms of the soil microbial effects on C. squarrosa. Key Results The soil sterilization treatment significantly increased the biomass of L. chinensis and C. squarrosa in both monoculture and mixture conditions, which indicated that the soil microbiota had negative growth effects on both plants. The addition of P neutralized the negative microbial effects for both L. chinensis and C. squarrosa , whereas the mixture treatment amplified the negative microbial effects on L. chinensis but alleviated them on C. squarrosa. Transcriptomic analysis from C. squarrosa roots underscored that the negative soil microbial effects were induced by the upregulation of defence genes. The P addition treatment resulted in significant decreases in the number of differentially expressed genes attributable to the soil microbiota, and some defence genes were downregulated. Conclusions Our results underline that indigenous soil microbiota have negative effects on the growth of two dominant plant species from a semiarid steppe, but their effects are highly dependent on the soil P availability and planting patterns. They also indicate that defence genes might play a key role in controlling plant growth responses to the soil microbiota. [ABSTRACT FROM AUTHOR]

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Plant invasion has severely damaged ecosystem stability and species diversity worldwide. The cooperation between arbuscular mycorrhizal fungi (AMF) and plant roots is often affected by changes in the external environment. Exogenous phosphorus (P) addition can alter the root absorption of soil resources, thus regulating the root growth and development of exotic and native plants. However, it remains unclear how exogenous P addition regulates the root growth and development of exotic and native plants mediated by AMF, affecting the exotic plant invasion. In this experiment, the invasive plant Eupatorium adenophorum and native plant Eupatorium lindleyanum were selected and cultured under intraspecific (Intra-) competition and interspecific (Inter-) competition conditions, involving inoculation with (M+) and without AMF (M−) and three different levels of P addition including no addition (P0), addition with 15 mg P kg−1 soil (P15), and addition with 25 mg P kg−1 soil (P25) for the two species. Root traits of the two species were analyzed to study the response of the two species' roots to AMF inoculation and P addition. The results showed that AMF significantly promoted the root biomass, length, surface area, volume, tips, branching points, and carbon (C), nitrogen (N), and P accumulation of the two species. Under M+ treatment, the Inter- competition decreased the root growth and nutrient accumulation of invasive E. adenophorum but increased the root growth and nutrient accumulation of native E. lindleyanum relative to the Intra- competition. Meanwhile, the exotic and native plants responded differently to P addition, exhibiting root growth and nutrient accumulation of invasive E. adenophorum increased with P addition, whereas native E. lindleyanum reduced with P addition. Further, the root growth and nutrition accumulation of native E. lindleyanum were higher than invasive E. adenophorum under Inter- competition. In conclusion, exogenous P addition promoted the invasive plant but reduced the native plant in root growth and nutrient accumulation regulated by AMF, although the native plant outcompeted the invasive plant when the two species competed. The findings provide a critical perspective that the anthropogenic P fertilizer addition might potentially contribute to the successful invasion of exotic plants. [ABSTRACT FROM AUTHOR]

Human activities and global climate change have greatly increased nitrogen (N) and phosphorus (P) inputs and altered precipitation patterns in alpine meadows. Functional genes are important indicators of microorganisms that drive the nitrogen cycling process; however, the functional gene responses of soil nitrogen cycling to soil N and P availability and drought remain unclear. Separate or combined treatments of nitrogen and phosphorus fertilization and drought were conducted on the Zoige Wetland in the Qinghai-Tibet Plateau, and the abundances of nitrification functional genes AOA amoA and AOB amoA and denitrification functional genes nirS, nirK, and nosZ were measured to explore the response of functional genes to these treatments. Seven treatments, including control (CK), N addition (N), P addition (P), 50% reduction in precipitation (D), N and P addition (NP), N addition with drought (ND), and NP addition with drought (NPD), were investigated. The results indicated that N application significantly increased AOB amoA abundance, while P application and drought had no significant effects on the abundance of functional genes. The combined treatment of N and P addition and drought increased AOB amoA abundance but did not significantly affect AOA amoA abundance, suggesting that AOB amoA was more responsive to soil N and P availability and moisture change than AOA amoA. However, the abundance of denitrification functional genes was not affected by these treatments. Denitrification functional genes were less sensitive to soil N and P availability and moisture change than nitrification functional genes. The integrated effects of N addition, P addition, and drought did not affect the abundance of the above N cycling functional genes. These results indicate that AOB amoA may play a more critical role in the process of ammonia oxidation than AOA amoA in alpine meadows, and the denitrification genes (nirK, nirS, and nosZ) were better than ammoxidation genes (AOA and AOB) at adapting to the soil environmental changes caused by increasing N and P deposition and drought in alpine meadows. [ABSTRACT FROM AUTHOR]

The decoupling of microbial functional and taxonomic components refers to the phenomenon that a drastic change in microbial taxonomic composition leads to no or only a gentle change in functional composition. Although many studies have identified this phenomenon, the mechanisms underlying it are still unclear. Here we demonstrate, using metagenomics data from a steppe grassland soil under different grazing and phosphorus addition treatments, that there is no “decoupling” in the variation of taxonomic and metabolic functional composition of the microbial community within functional groups at species level. In contrast, the high consistency and complementarity between the abundance and functional gene diversity of two dominant species made metabolic functions unaffected by grazing and phosphorus addition. This complementarity between the two dominant species shapes a bistability pattern that differs from functional redundancy in that only two species cannot form observable redundancy in a large microbial community. In other words, the “monopoly” of metabolic functions by the two most abundant species leads to the disappearance of functional redundancy. Our findings imply that for soil microbial communities, the impact of species identity on metabolic functions is much greater than that of species diversity, and it is more important to monitor the dynamics of key dominant microorganisms for accurately predicting the changes in the metabolic functions of the ecosystems. [ABSTRACT FROM AUTHOR]

Plants can alter soil microbial biomass and extracellular enzyme activities related with carbon (C), nitrogen (N), and phosphorus (P), through litter and root exudates, with consequences on soil carbon, nitrogen and phosphorus (P) cycling. However, it is not well known how the changes in soil phosphorus availability affect the relationships between plants and soil microorganisms. In this study, a factorial experiment was conducted to investigate the effects of Chinese fir (Cunninghamia lanceolata) planting and different levels of P addition (0, 1.95, 3.9, 7.8 and 15.6 g P ⋅ m-2 ⋅ a-1)on soil microbial biomass and extracellular enzyme activities. The results showed that planting Chinese fir planting significantly altered soil microbial biomass and C- and N- and P-related extracellular enzyme activities, but the effects were dependent on P addition levels. Without P addition, Chinese fir planting significantly reduced soil nutrient availability and pH, which led to the aggravation of P limitation and lower soil microbial biomass. P addition relieved P limitation, and reduced soil acid phosphatase (ACP) activities by 30.0%, 30.5%, 35.3% and 47.1% with the increasing P addition level (1.95, 3.9, 7.8 and 15.6 g P ⋅ m-2 ⋅ a-1). Under three P addition levels (1.95, 3.9 and 7.8 g P ⋅ m-2 ⋅ a-1), the negative effects of Chinese fir planting on soil microbial growth were alleviated. Under the high P addition level (15.6 g P ⋅ m-2 ⋅ a-1), the negative effects of Chinese fir planting on soil microbial growth occurred again due to soil N limitation. Taken together, Chinese fir planting and soil P availability generally affected soil microbial biomass and extracellular enzyme activities, and changed P limitation. [ABSTRACT FROM AUTHOR]

磷素的大量输入，将显著影响陆地生态系统的碳平衡和碳固存，为探究陇中黄土高原旱作农田土壤呼吸及其组分动态变 化特征与碳平衡对磷添加的响应，采用完全随机区组设计，设不施磷肥（CK）、低磷（P1）、中磷（P2）、高磷（P3）4个施磷水平，测定春 小麦生育期各处理土壤呼吸及其组分与环境因子，计算土壤呼吸温度敏感性指数、净生态系统生产力与碳平衡。研究结果表明， 磷添加增加了土壤呼吸及其组分的 CO2排放量。与 CK 处理相比，P1、P2处理和 P3处理土壤呼吸 CO2累计排放量分别显著增加 13.85%、24.86% å’Œ 26.47%（P<0.05）；土壤异养呼吸显著提高了 9.09%、9.4% å’Œ 14.52%（P<0.05）；土壤自养呼吸分别提高了 18.96%、39.98%å’Œ38.33%（P<0.05）。土壤呼吸及其组分受到多因素的共同作用，拟合分析结果表明，土壤水分和温度分别可解释 土壤呼吸及其组分速率变异的 37.0%~49.7% å’Œ 69.4%~76.8%。逐步回归和方差分解结果表明，土壤呼吸的主要影响因素为 0~5 cm土壤碱性磷酸酶和0~10 cm土壤有机碳；异养呼吸的主要影响因素为0~5 cm土壤β-1，4-葡萄糖苷酶、0~5 cm土壤纤维素二糖 水解酶和5~10 cm土壤碱性磷酸酶；自养呼吸的主要影响因素为0~5 cm土壤碱性磷酸酶、0~5 cm土壤速效磷、0~5 cm土壤有机碳 å’Œ 5~10 cm 土壤纤维素二糖水解酶。CK、P1、P2处理和 P3处理的净生态系统生产力均为正值，其数值分别为 2 640.10、3 412.91、 3 579.83 kg·hm-2 å’Œ3 790.74 kg·hm-2 ，均表现为土壤碳的“汇”。因此，在陇中黄土高原旱作农田生态系统管理中，应合理地增施磷 肥（建议施用115 kg·hm-2 ），提高土壤固碳效率，科学合理地构建环境保护与经济高效并重的现代化农业生产管理体系。 磷素的大量输入，将显著影响陆地生态系统的碳平衡和碳固存，为探究陇中黄土高原旱作农田土壤呼吸及其组分动态变 化特征与碳平衡对磷添加的响应，采用完全随机区组设计，设不施磷肥（CK）、低磷（P1）、中磷（P2）、高磷（P3）4个施磷水平，测定春 小麦生育期各处理土壤呼吸及其组分与环境因子，计算土壤呼吸温度敏感性指数、净生态系统生产力与碳平衡。研究结果表明， 磷添加增加了土壤呼吸及其组分的 CO2排放量。与 CK 处理相比，P1、P2处理和 P3处理土壤呼吸 CO2累计排放量分别显著增加 13.85%、24.86% 和 26.47%（P<0.05）；土壤异养呼吸显著提高了 9.09%、9.4% 和 14.52%（P<0.05）；土壤自养呼吸分别提高了 18.96%、39.98%和38.33%（P<0.05）。土壤呼吸及其组分受到多因素的共同作用，拟合分析结果表明，土壤水分和温度分别可解释 土壤呼吸及其组分速率变异的 37.0%~49.7% 和 69.4%~76.8%。逐步回归和方差分解结果表明，土壤呼吸的主要影响因素为 0~5 cm土壤碱性磷酸酶和0~10 cm土壤有机碳；异养呼吸的主要影响因素为0~5 cm土壤β-1，4-葡萄糖苷酶、0~5 cm土壤纤维素二糖 水解酶和5~10 cm土壤碱性磷酸酶；自养呼吸的主要影响因素为0~5 cm土壤碱性磷酸酶、0~5 cm土壤速效磷、0~5 cm土壤有机碳 和 5~10 cm 土壤纤维素二糖水解酶。CK、P1、P2处理和 P3处理的净生态系统生产力均为正值，其数值分别为 2 640.10、3 412.91、 3 579.83 kg·hm-2 和3 790.74 kg·hm-2 ，均表现为土壤碳的“汇”。因此，在陇中黄土高原旱作农田生态系统管理中，应合理地增施磷 肥（建议施用115 kg·hm-2 ），提高土壤固碳效率，科学合理地构建环境保护与经济高效并重的现代化农业生产管理体系。 [ABSTRACT FROM AUTHOR]

Both temperature and nutrient availability have essential roles in regulating the decomposition of soil carbon (C) and nitrogen (N), the main controls on organic matter accumulation in forest ecosystems. However, there is a lack of information about how N deposition and phosphorus (P) additions might impact soil C and N decomposition rates in subtropical forests under climate warming. We measured soil organic C and N mineralisation rates and corresponding exoenzyme activities in a subtropical forest soil that had received N and/or P additions for six years in experimental conditions at a range of temperatures between 10 and 40°C. Our results showed that soil organic C and N decomposition rates were positively correlated with the activities of their corresponding enzymes, which suggests that the extracellular enzyme activities could be the main influence on soil organic matter (SOM) decomposition rates. N additions had a significant positive effect on soil organic C mineralisation and enhanced oxidase and hydrolase activities. P additions had little effect on soil organic C and N decomposition rates. These results challenge the assumptions that soil microorganisms are N‐rich and P availability restricts organic matter decomposition, and provides additional evidence that N, not P, regulates organic matter decomposition in subtropical forests. While N additions significantly influenced the soil C and N decomposition rates, they had little effect on their sensitivity to temperature. In contrast, P additions had a significant effect on the temperature sensitivities of SOM decomposition and the βG and NAG Vmax. Overall, our results show that SOM decomposition is vulnerable to both N and P additions, and both should be considered when predicting how SOM decomposition and C cycling might change under warming. Highlights: The effect of N and/or P additions on the temperature sensitivity of SOM decomposition was explored.N stimulated soil organic C decomposition rates and corresponding enzyme activities.P promoted the sensitivity of SOM decomposition to temperature changes.N and P additions could affect the stability of SOM in subtropical forests in the future. [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen(N) deposition increased soil active N, and excessive N content led to the increase of the ratio of nitrogen to phosphorus (N: P), which changed plant growth from N limitation to phosphorus(P) limitation. Potentilla is not only an important native greening material, but also a common diversity component in various grasslands in China. Its population fluctuation in the process of N deposition will affect the species diversity and productivity of grassland ecosystem. Potting experiment was conducted for 2 years with Potentilla tanacetifolia, a common species in the northern warm steppe, as the material. Through the interactive treatment of different N addition (0, 10, 20, 40 kg N ha yr−1) and P addition (4, 6, 8 kg P ha yr−1) gradients, to analysis the feedback effect between leaf N and P content and net photosynthetic rate (Pn). We explored the N: P threshold of N and P limitation from the perspective of Pn. The results showed that: 1) Under low soil N concentration, P addition can promote N absorption of P.tanacetifolia, while the high soil N concentration can reduce the N: P by increasing the leaf P content to weaken the limiting effect caused by nutrient imbalance of plants. 2) In N addition environment, proper P addition increased Pn by increasing stomatal conductance (Gs), while excessive P addition decreased Gs and inhibited Pn. 3) The Pn showed a single peak normal distribution characteristic with the enhancement of the N: P of leaves, and the Pn was at a high level between 14.5–17.0. It was preliminarily believed that the threshold value of N: P in leaves of P.tanacetifolia was 14.5–17.0. Plant photosynthesis is very sensitive to the environment and easy to be affected by the external environment. The results of N and P addition showed that Pn of broad-leaf forbs was easily affected by N and P restriction, and P addition increased Pn of broad-leaf forbs under N restriction. There was a certain relationship between N:P and Pn. It was preliminarily believed that the N: P of P.tanacetifolia leaves is not limited by nitrogen and phosphorus in the range of 14.5-17.0.

Purpose: Grasslands are the most extensive vegetation type in the terrestrial ecosystem and have an important role in the soil phosphorus (P) cycle. Many nutrient addition and warming experiments have been conducted in grasslands; however, the global pattern of nutrient addition and experimental warming impacts on soil P cycle is unclear. Methods: We conducted a meta-analysis of 68 publications to synthesize the mechanisms underlying global grassland ecosystem responses to nutrient addition and experimental warming. Results: Our analysis indicated that nitrogen (N) addition reduced microbial biomass P (− 11.2%) but increased litter P concentration (+ 15.5%) and available P (+ 14.2%). Experimental warming reduced microbial biomass P (− 10.5%) and available P (− 6.7%) but increased litter P concentration (+ 46.2%). P addition increased available P (+ 222.3%) and microbial biomass P (+ 98.1%). The available P response to nutrient addition and experimental warming was more sensitive in temperate grasslands than in alpine grasslands. The responses of soil total and available P to nutrient addition depended on environmental conditions such as air temperature and soil pH. Conclusion: Our results suggest that N addition may promote P mineralization and possibly stimulate the transformation of refractory or resistant forms of soil inorganic P, whereas experimental warming accelerates the P cycle by regulating plant acquisition and enzyme activity. Environmental factors (e.g., temperature, precipitation, pH) affect the soil P response to nutrient addition by altering microbial and enzymatic activities. It is crucial to understand the dynamic changes in soil microbial and enzyme activities to predict the P cycle in grassland soils in the future. [ABSTRACT FROM AUTHOR]

Background and aims: The amount of nitrogen (N) derived from symbiotic N2 fixation by legumes in grasslands might be affected by anthropogenic N and phosphorus (P) inputs, but the underlying mechanisms are not known. Methods: We evaluated symbiotic N2 fixation in 17 natural and semi-natural grasslands on four continents that are subjected to the same full-factorial N and P addition experiment, using the 15N natural abundance method. Results: N as well as combined N and P (NP) addition reduced aboveground legume biomass by 65% and 45%, respectively, compared to the control, whereas P addition had no significant impact. Addition of N and/or P had no significant effect on the symbiotic N2 fixation per unit legume biomass. In consequence, the amount of N fixed annually per grassland area was less than half in the N addition treatments compared to control and P addition, irrespective of whether the dominant legumes were annuals or perennials. Conclusion: Our results reveal that N addition mainly impacts symbiotic N2 fixation via reduced biomass of legumes rather than changes in N2 fixation per unit legume biomass. The results show that soil N enrichment by anthropogenic activities significantly reduces N2 fixation in grasslands, and these effects cannot be reversed by additional P amendment. [ABSTRACT FROM AUTHOR]

Rhizosphere is a hot zone formed by root–microbial interaction, and microbial activities in this zone differ from those in bulk soil. Nitrogen (N) and phosphorus (P) inputs are able to change forest soil nutrient availability, affecting microbial communities and extracellular enzyme secretion. However, the impact of N and P additions on the structure and functions of rhizosphere microbial community in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantations are not yet clear. To reveal the impact of short-term N and P inputs on microbial community structure and functions in rhizosphere soil, soil physicochemical properties, phospholipid fatty acids, and seven hydrolytic enzyme activities were measured in Chinese fir rhizosphere soil after one year of nutrient addition. N addition reduced the rhizosphere’s pH and increased ammonium N, but the rhizosphere’s available N (AN) initially wentdown and then up along the P-addition gradient. The rhizosphere fungi:bacteria ratio showed a decline after N addition, while a concave peak change occurred as rhizosphere AN under P addition. Moreover, rhizosphere extracellular enzyme activities and microbial C limitation climbed markedly with N addition rates, while this also showed an obviously unimodal pattern along the P-addition gradient. P addition did not alleviate rhizosphere microbial P limitation. Our findings suggest inconsistent responses of rhizosphere microorganisms of Chinese fir soil to N and P additions. Rhizosphere N availability can regulate microbial community structure and extracellular enzymes by influencing microbial C limitation. The study provides more knowledge on microbial activities in rhizosphere soil of subtropical forests under global changes.

Phosphorus (P) fertilizer is commonly used in subtropical plantations to augment nutrients including carbon (C), nitrogen (N), and P to maintain plants engaged in metabolism. Stoichiometric homeostasis reflects the adaptation of plants to various environments (including P fertilizer supply rates). It is thus of great significance to understand C:N:P stoichiometry in the plant–litter–soil system under P addition and the stoichiometric homeostasis of plant tissues for the P fertilization management of slash pine (Pinus elliottii Engelm) plantations. In subtropical China, we measured the C, N, and P contents in root, branch, needle, litter, and soil in slash pine plantations fertilized with four treatments, P1 (25 kg P ha1 yr1), P2 (50 kg P ha1 yr1), P3 (100 kg P ha1 yr1), and a control (CK), and calculated the stoichiometric homeostasis of plant tissues. The results show that P3 treatment increased the C, N, and P contents of the needle. P2 and P3 treatments increased the P content of the litter and the N:P ratio of the root while decreasing the C:N ratio of the root. P addition treatments increased C and P element accumulation in soil but had no effect on soil stoichiometry. The nutrient contents of needle and branch were higher than those of root and litter, indicating that slash pine was more inclined to allocate nutrients to the aboveground tissues. The stoichiometric homeostasis of C, N, and P among plant tissues was graded as follows: root > branch > needle. The needle’s nutritional homeostasis was C > N > P, with 1/H values of 0.08, 0.34, and 0.74, respectively. These findings demonstrate that during P addition, the C, N, and P stoichiometric homeostasis varied among plant tissues and element types. In conclusion, P application altered nutrient distribution in the plant–litter–soil system, alleviating P restriction in slash pine forests in southern China. P addition levels should be finely adjusted in the future for longer-term observation trials, and the trade-off between P addition rates and economic and ecological advantages should be properly examined.

Plant invasion has severely damaged ecosystem stability and species diversity worldwide. The cooperation between arbuscular mycorrhizal fungi (AMF) and plant roots is often affected by changes in the external environment. Exogenous phosphorus (P) addition can alter the root absorption of soil resources, thus regulating the root growth and development of exotic and native plants. However, it remains unclear how exogenous P addition regulates the root growth and development of exotic and native plants mediated by AMF, affecting the exotic plant invasion. In this experiment, the invasive plant Eupatorium adenophorum and native plant Eupatorium lindleyanum were selected and cultured under intraspecific (Intra-) competition and interspecific (Inter-) competition conditions, involving inoculation with (M+) and without AMF (M−) and three different levels of P addition including no addition (P0), addition with 15 mg P kg−1 soil (P15), and addition with 25 mg P kg−1 soil (P25) for the two species. Root traits of the two species were analyzed to study the response of the two species’ roots to AMF inoculation and P addition. The results showed that AMF significantly promoted the root biomass, length, surface area, volume, tips, branching points, and carbon (C), nitrogen (N), and P accumulation of the two species. Under M+ treatment, the Inter- competition decreased the root growth and nutrient accumulation of invasive E. adenophorum but increased the root growth and nutrient accumulation of native E. lindleyanum relative to the Intra- competition. Meanwhile, the exotic and native plants responded differently to P addition, exhibiting root growth and nutrient accumulation of invasive E. adenophorum increased with P addition, whereas native E. lindleyanum reduced with P addition. Further, the root growth and nutrition accumulation of native E. lindleyanum were higher than invasive E. adenophorum under Inter- competition. In conclusion, exogenous P addition promoted the invasive plant but reduced the native plant in root growth and nutrient accumulation regulated by AMF, although the native plant outcompeted the invasive plant when the two species competed. The findings provide a critical perspective that the anthropogenic P fertilizer addition might potentially contribute to the successful invasion of exotic plants.

Phosphorus (P) availability affects the accumulation and enrichment of soil nitrogen (N) forms. However, the effect of P addition on the distribution and turnover of soil N forms in the mustard–maize rotation system is unclear. A field experiment is conducted to investigate the effect of P addition on the turnover of soil N forms in a mustard–maize rotation system. The results show that after maize harvesting, the levels of ammonium N in soil with P addition are smaller compared to those without P addition. The organic N forms in soil with P addition are greater compared without P addition after mustard harvest. Moreover, the hydrolysable ammonium N and unknown hydrolysable N in soil with P addition are smaller than those without P addition after maize harvest. Structured equation model results show the intensities of hydrolysable amino acid N, hydrolysable amino sugar N, and unknown hydrolysable N transformed into ammonium N in soil with P addition are greater than those without P addition, and the intensities of these organic N forms transformed into nitrate N are weaker. The results indicate that P addition affect the accumulation and enrichment of soil N by altering the turnover of soil N forms. [ABSTRACT FROM AUTHOR]

Increased nitrogen (N) inputs in subtropical forest ecosystems were widely reported. Extra N additions were reported to cause nutrient imbalance and phosphorus (P) limitation in many tropical and subtropical forests, and further result in changes in soil nitrous oxide (N2O) and methane (CH4) fluxes. Here, we conducted experiments with N (high N addition: 15 g N/m2, HN), P (low: 5 g P/m2, LP; high: 15 g P/m2, HP) and their interactive (HNLP and HNHP) treatments to investigate how N and P additions affected CH4 and N2O exchanges in an N-rich Chinese fir plantation (Cunninghamia lanceolata), and further explored the underlying mechanisms through the structural equation model (SEM) analysis. The results indicated that N addition alone (HN) significantly (p < 0.05) increased the soil N2O emissions by 30.15% and 80.47% over annual and 4-month periods, mainly owing to the elevated NH4+-N content. P addition alone (LP and HP) did not significantly affect the soil N2O emissions as compared with the control. The SEM analysis indicated that increased N2O emissions under N addition were primarily explained by the increase in available N and contributed more to the stimulated NH4+-N contents. N and P interactive additions slightly (not significant) stimulated the N2O emissions as compared with that under the N addition alone treatment. High-dose P addition significantly increased the soil CH4 uptake by 15.80% and 16.23% under the HP and HNHP treatments, respectively, while N addition alone and low P addition (LP and HNLP) did not significantly affect CH4 uptake as compared with the control. The increased water-soluble organic carbon and microbial biomass carbon explained the increased CH4 uptake under high P addition. The fertilization effects on N2O emissions and CH4 uptake mainly occurred in the first 4 months and diminished after that. Our results suggested that the direction, magnitude and timing of the N and P addition effects on N2O emissions and CH4 uptake would depend on the soil nutrient status and plant–microbial competition for N and P in subtropical forests. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is considered to be one of the most limiting elements in terrestrial ecosystems, especially in the subtropical forests in China. However, little is known about how rhizosphere soil bacterial communities and functions, especially at the level of functional genes abundance, respond to P inputs. Herein we conducted a P addition experiment and treatments included 80 g m−2 yr−1 (P1), 160 g m−2 yr−1 (P2), 240 g P m−2 yr−1 (P3), 320 g P m−2 yr−1 (P4) and the control without any fertilizer application (CK) in the Phoebe bournei young plantations. This study used the quantitative microbial element cycling (QMEC) smart chip technology and 16S rRNA gene sequencing to investigate changes in the relative abundance of C-, N-, and P-cycle genes and rhizosphere soil bacterial community that received various inputs of P nutrients. Soil bacterial diversity showed a progressively decreased trend with increasing of P fertilizer, accompanied by significant differences in bacterial community structure between CK and P4 treatment. The relative abundance of N- and P-cycle genes were increased by P addition, and the highest relative abundance was observed in P3 treatment among the five P addition treatments. The relative abundance of C-cycle genes was significantly enhanced by P4 treatment, promoting C fixation, degradation, and methane metabolism. Random forest model indicated that invertase activity was the most important predictor for the relative abundance of C-, N-, and P-cycle genes. Partial least squares path modeling analysis revealed that the predominant effect of P fertilizer in driving the relative abundance of functional genes was maintained when accounting for multiple abiotic factors (total P, available P, available potassium, soil organic carbon and soil pH) drivers and there was a strong relationship between the relative abundance of functional genes and catalase, invertase and urease activities. Overall, our findings confirm that high P addition significantly altered rhizosphere soil bacterial community composition in the Phoebe bournei young plantations, and significantly enhanced the relative abundance of C-, N- and P-cycle genes. These results suggest that sufficient P fertilizer benefits to improve the nutrients cycle processes mediating by soil bacteria in Phoebe bournei young plantations. [Display omitted] • Soil bacterial diversity showed a progressively decreased trend with increasing of P fertilizer. • High P addition increased the relative abundance of functional genes involving in C-, N- and P-cycle genes. • TP, AP, AK, SOC and pH had significant effects on the relative abundance of functional genes. • Enzyme activities were significantly correlated with the relative abundance of functional genes. • Invertase activity was the most important predictor for the relative abundance of functional genes. [ABSTRACT FROM AUTHOR]